Method and forming machine for deforming a hollow workpiece

ABSTRACT

The invention relates to a method and a forming apparatus for deforming a hollow workpiece having at least one open end, wherein the workpiece is clamped down in a clamping device, a first forming tool is placed into contact with the outer surface of the workpiece, said workpiece and said tool are rotated about an axis of rotation relative to each other and said workpiece is deformed by means of said first tool. A second forming tool is placed into the cavity defined by the workpiece and into contact with the inner surface of the hollow workpiece, after which the workpiece is deformed by means of said second tool.

[0001] The invention relates to a method for deforming a hollowworkpiece having at least one open end, such as a metal cylinder, forexample, wherein the workpiece is clamped down in a clamping device, afirst forming tool is placed into contact with the outer surface of theworkpiece, the workpiece and the tool are rotated about an axis ofrotation relative to each other and the workpiece is deformed by meansof said first tool. The invention furthermore relates to a formingmachine in accordance with the preamble of claim 8, by means of which ahollow workpiece having at least one open end can be deformed.

[0002] Such a method and apparatus are known, for example from Europeanpatent application no. EP 0 916 428. Said publication discloses a methodand a forming machine, comprising a forming head fitted with a number ofrollers, by means of which the diameter of one end of a cylindricalmetal element is reduced and moreover bent through an angle.

[0003] To this end, the metal cylinder is clamped down and said cylinderand said forming head are rotated relative to each other about an axisof rotation, whereupon said end is deformed by pressing said rollers inradial direction against the outer surface of said cylinder and movingthem along said outer surface in a number of cycles, whereby the radialdistance between the rollers and the axis of rotation is decreased witheach cycle, as a result of which a reduction of the diameter isobtained. Since the axis of rotation is at an angle with the centralaxis of the metal cylinder, the end of the cylinder is not only reducedas a result of the movement in radial direction of the rollers, but inaddition said end will also be positioned at an angle. Due to the use ofthe aforesaid cycles, the workpiece assumes the shape of the finalproduct step by step.

[0004] EP 0 916 426 discloses a comparable method and forming machine,wherein the axis of rotation is eccentrically offset from the centralaxis of the metal cylinder. Thus a product is obtained wherein thecentral axis of the deformed portion is likewise offset from the centralaxis of the undeformed portion of the metal cylinder.

[0005] The method and apparatus in hand can be used, for example, in theproduction of the housings of catalytic converters that form part of theexhaust system of vehicles, such as passenger cars. Such catalyticconverters have a diameter which is larger than the diameter of thepipes of the exhaust system of which they form part, and they arepreferably positioned close to the engine block in order to reach theiroperating temperature as quickly as possible after the engine has beenstarted and to maintain that temperature as much as possible. Oneconsequence of this is that, first of all, the diameter of theconnections on either side of the catalytic converter housing must bereduced in order to properly connect to the rest of the exhaust systemand that in addition they often need to have a complicated shape inorder to enable an optimum position with respect to the engine block.

[0006] Prior art methods and apparatuses for producing workpieces havingat least one deformed end, such as e.g. the above-described catalyticconverter housings, appear to provide insufficient freedom as regardsshaping. Moreover, it is necessary to use relatively thick-walledworkpieces, since a heavy load is exerted on the material during thedeformation process, which may lead to folds, cracks and/or an irregulardistribution of the wall thickness of the final product. As a result,the obtained products, such as e.g. the aforesaid catalytic converterhousings, are often heavier than is necessary for their properfunctioning in an exhaust system.

[0007] It is an object of the present invention to eliminate the abovedrawbacks or at least to alleviate them to a significant extent.

[0008] In order to accomplish that objective, the method as referred toin the first paragraph is characterized in that a second forming tool isplaced into the cavity defined by the workpiece and into contact withthe inner surface of the hollow workpiece, and the workpiece is deformedby means of said second tool. The forming machine according to thepresent invention is characterized in that it comprises at least onesecond forming tool, and possibly driving means for rotating said secondtool, which second tool can be introduced into the workpiece and placedinto contact with the inner wall of the workpiece in such a manner thatsaid wall can be deformed in outward direction, i.e. in a direction awayfrom the cavity defined by the workpiece.

[0009] The use of the second forming tool, such as preferably one ormore forming rollers, provides greater freedom as regards design and itmakes it possible to deform the workpiece in such a manner that thedeformed portions extend outside the diameter of the original workpiece,which is not possible with the method and apparatus according to theabove-described prior art. If the workpiece is a metal cylinder, thismeans that after deformation, the deformed end(s) will lie partially orentirely outside the circumference of the undeformed part of the metalcylinder.

[0010] Moreover, the load that is exerted on the workpiece during thedeformation process can be considerably reduced, so that it will bepossible to form workpieces having a relatively small wall thickness aswell. A minimum wall thickness of the cylindrical starting material of1.5 mm is frequently used for the aforesaid housings for catalyticconverters, whilst the invention makes it possible to deform materialshaving a smaller wall thickness of, for example, 1.2 mm or less.

[0011] Complex shapes can be obtained by pivoting the clamping device onthe one hand and the tools on the other hand relative to each otherabout at least one axis during said deformation and/or between deformingsteps (on the same workpiece). Pivoting about two or more axes, whereinat least two of said axes, or the projections of each of said axes on acommon plane, are at an angle (for example of 90°) with respect to eachother, makes it possible to produce complex shapes in variousdirections.

[0012] The invention furthermore relates to a hollow workpiece having acontinuous wall and at least one open end, which has been deformed,preferably by means of the above-described method, wherein at least partof the edge of said end lies outside the circumference of the workpieceafter deformation. Such a workpiece preferably comprises a substantiallycylindrical or oval metal body or at any rate a body which can bedeformed by means of the present method, having two open ends which havebeen deformed in such a manner that at least part of the edge of atleast one of the two ends lies outside the circumference of anundeformed portion of the workpiece, wherein the projections of thecentral axes of said ends on a plane straight through an undeformed partof the metal body are at an angle of less than 180° with respect to eachother.

[0013] In addition to this, the invention relates to a catalyticconverter for a vehicle, such as e.g. a car, comprising such aworkpiece.

[0014] For the sake of completeness, it is noted that Japanese patentapplication no. 08-224625 describes the manner in which the diameter ofthe neck of a can is reduced by means of forming rollers whilst adetainer is present in the can. Said detainer only functions to supportthe inner surface of the neck of the can, it is not used for deformingsaid neck.

[0015] The invention will now be explained in more detail with referenceto the appended figures, which show a number of embodiments of themethod and the apparatus according to the present invention.

[0016]FIG. 1 is a schematic top plan view, partially in section, of aforming machine according to the present invention, comprising twoforming heads and a stationary workpiece.

[0017]FIG. 2 is a side elevation of the forming machine of FIG. 1.

[0018]FIG. 3 is a side elevation of the forming machine of FIG. 1,wherein a part of the forming machine is turned through an angle of 90°.

[0019]FIGS. 4 and 5 schematically show a number of stages of a methodaccording to the present invention, carried out on the forming machineof FIG. 1.

[0020]FIGS. 6 and 7 are schematic top plan views, partially in section,of a second embodiment of the forming machine according to the presentinvention comprising a single forming head and a rotatable workpiece.

[0021]FIG. 8 is a schematic top plan view, partially in section, of avariant of the forming machine according to FIGS. 6 and 7.

[0022]FIG. 9 shows a number of stages of a second method according tothe present invention, carried out on the forming machine of FIGS. 6 and7.

[0023]FIGS. 10, 11 and 12 are schematic top plan views, partially insection, of a fourth embodiment of the forming machine according to thepresent invention, by means of which the workpiece can be rotated.

[0024]FIGS. 13 and 14 schematically show a number of stages of a secondmethod according to the present invention, carried out on the formingmachine of FIGS. 10-12.

[0025] Parts corresponding to each other or having substantially thesame function in the various embodiments will be indicated by the samenumerals.

[0026]FIG. 1 shows a forming machine 1, comprising a first forming head2, a second forming head 3 and a chuck 4 for clamping down theworkpiece, for example the illustrated, already deformed, metal cylinder5. The two forming heads 2, 3 comprise a baseplate 6 on which two guiderails 7 are mounted. Guides 8 extend over said rails 7 on which guides asecond set of guide rails 9 is mounted, which guide rails extend atright angles to said first rails 7. Present on said second set of railsare guides 10, which support a housing 11, in which an assembly 12,comprising forming rollers 13 and means for moving said forming rollers13, is mounted in bearings 14.

[0027] Each of the forming rollers 13 is rotatably mounted on one end ofa rod 15, which is in turn mounted on or forms part of a wedge-shapedelement 16, which widens in the direction of forming rollers 13. Formingrollers 13 and their respective rods 15 and wedge-shaped elements 16 caneach be moved radially inwards and outwards relative to the axis ofrotation 17 of assembly 12. To this end, each of the wedge-shapedelements 16 is mounted on a wedge-shaped guiding mandrel 18, whosethickness decreases linearly in the direction of forming rollers 13, insuch a manner that wedge-shaped elements 16, and thus rods 15 androllers 13, are forced radially towards axis of rotation 17 upon outwardmovement (to the right in the drawing) of mandrels 18, and radially awayfrom axis of rotation 17 upon inward movement (to the left in thedrawing) thereof.

[0028] In accordance with the invention, assembly 12 furthermorecomprises a forming roller 19 (hereinafter called inside roller 19),which is mounted in assembly 13 in substantially the same manner asforming rollers 13, i.e. rotatably mounted on one end of a rod 20, whichis in turn mounted on or forms part of a wedge-shaped element 21, whichwidens in the direction of forming inside roller 19. The element 21 ismounted on a wedge-shaped mandrel 22, in such a manner that the element21, and thus rod 20 and roller 19 are forced radially towards the axisof rotation 17 upon outward movement of mandrel 22 and radially awayfrom axis of rotation 17 upon inward movement thereof.

[0029] In FIG. 1, inside roller 19 has been moved into workpiece 5 andhas been placed into contact with the inner wall of workpiece 5. Thewall of workpiece 5 can be deformed in outward direction, that is, inradial direction away from the cavity 5 defined by workpiece 5, by meansof said inside roller 19. Forming rollers 13 and inside roller 19 oftenlie in the same plane, which plane extends perpendicularly to axis ofrotation 17 in this embodiment, so that the wall is confined betweensaid rollers 13, 19 at the location of the deformation.

[0030] Assembly 12 comprises an external gear 25 on a side remote fromrollers 13, 19, which gear mates with a pinion 26 mounted on the end ofa drive shaft 27 of an electric motor 28. Thus, the assembly 12 can berotated by means of electric motor 28.

[0031] Assembly 12 furthermore comprises a hydraulic cylinder 29, whichis capable of moving ring 18, and thus forming rollers 13, in radialdirection by means of a piston 30, a piston rod 31 and a pressure plate32. Within the framework of the present description, the radial movementof the forming rollers 13 will be indicated as the Z-direction.

[0032] Ring 22, and thus inside roller 19, can be moved in radialdirection by means of a hydraulic cylinder 33 and a hollow piston rod34, whilst housing 11 can be moved along said guide rails 7 and 9 in itsentirety by means of hydraulic cylinders 35 and 36. Within the frameworkof the present description, the radial movement of inside roller 19 willbe indicated as the W-direction. Movements of housing 11 parallel toaxis of rotation 17 and perpendicularly to said axis 17 will beindicated as the X-direction and the Y-direction, respectively.

[0033] Second forming head 3 is practically identical to forming head 2,but it is furthermore capable of pivoting movement about a pivot point37, so that the end of workpiece 5 that is being worked by said forminghead 3 can be deformed through an angle of 90, for example. In addition,an assembly 38 is provided, by means of which axis 37 can be moved, aswill be explained in more detail hereafter.

[0034]FIGS. 4 and 5 schematically show in 25 steps the manner in whichan open end of a metal cylinder 5 can be deformed by means of forminghead 3 of forming machine 1 according to FIG. 1. At the same time, theother end of cylinder 5 can be worked by means of forming head 2. Step 1shows the starting position, wherein workpiece 5 is clamped down in achuck 4. Said end, which has already undergone a machining step andwhich has a smaller diameter than the other part of cylinder 5, is then(step 2) deformed by rotating assembly 12 and placing the formingrollers 13, 19 into contact with, respectively, the outer surface andthe inner surface of cylinder 5 and moving said rollers radially towardsaxis of rotation 17 and away from axis of rotation 17, respectively, andsimultaneously pivoting the forming head through an angle β about pivotpoint 37. The various driving means are thereby controlled in such amanner that a composite, flowing movement of the forming rollers 13, 19(in Z-direction and W-direction), assembly 13 (in X-direction andY-direction) and the forming head (through an angle β) is obtained, as aresult of which a bent portion 40 is formed.

[0035] After forming head 3 has been pivoted through an angle β, themovement of the assembly 12 in the X-direction is continued (step 3), sothat a cylindrical portion 41 remains, which portion has a smallerdiameter than the original open end of cylinder 5 and which extends atan angle β relative to the other part of cylinder 5.

[0036] Then (step 4) the forming rollers 13, 19 are moved radiallyoutwards and radially inwards, respectively, so that the contact betweensaid rollers 13, 19 and, respectively, the outer surface and the innersurface of the wall of cylinder 5 is broken. Assembly 12 is moved backalong cylindrical portion 41 in the X-direction and the Y-directionuntil the transition between the bent portion 40 and said cylindricalportion 41.

[0037] The above cycle is repeated by pivoting forming head 3 through anangle β and translating and adjusting assembly 12 (step 5, which issubstantially identical to step 2) and translating assembly 12 in theX-direction and the Y-direction (step 6, which is substantiallyidentical to step 3), wherein the diameter of the cylindrical portion 41is further reduced. Then the contact between said rollers and saidcylindrical portion 41 is broken, and the assembly is returned to thetransition area between bent portion 40 and cylindrical portion 41 (step7, which is substantially identical to step 4).

[0038] Depending on the characteristics of the workpiece, such as thewall thickness, the mechanical strength and stiffness and the elasticelongation, steps 2-4 are repeated until the desired reduction of thediameter and the desired angle, for example of 90, have been obtained.If the nature of the workpiece involves that the angle β must not belarger than, for example, 15 or 8 per cycle, a total number of,respectively, 6 and 12 cycles will be required for the said deformation.

[0039] After the operations that are shown in FIG. 4 have been carriedout, pivot point 37 is moved by means of assembly 38 to the startingposition as shown in FIG. 5 (step 13). The operation of FIG. 4 (steps2-12) are repeated (steps 14-25), wherein the angle β is of oppositesense, however, so that an S-bend is obtained in the end of cylinder 5.

[0040] As is shown in FIG. 3, the forming head 3 of forming machine 1 isfurthermore capable of pivoting movement about axis of rotation 17 offorming head 2, so that the bending of workpiece 5 is not limited tobending in one and the same imaginary plane. Pivoting of forming head 3about axis of rotation 17 between or during operations enables thecentral axis of the deformed portion of workpiece 5 to assume athree-dimensional shape.

[0041]FIGS. 6 and 7 show a second and relatively simple embodiment ofthe forming machine 1 according to the present invention, whereinworkpiece 5 is clamped down, in a manner which is known per se, in arotatable chuck 60 which is mounted in a spindle casing 61 and which canbe rotated about an axis 17 by means of an electric motor (not shown). Aforming head 62 comprises an assembly 12, which is stationary and whichneed not be rotated, although driving means may be provided, of course,if an exceptionally high rotational speed of the assembly 12 relative tothe workpiece 5 is desired. FIG. 8 shows a variant of the formingmachine 1 according to FIGS. 6 and 7, wherein forming rollers 13 andinside roller 19 each form part of their own assembly 12, 12′. Thismakes it possible to control inside roller 19 fully. independently offorming roller 13, which may be desirable for specific products.

[0042]FIG. 9 schematically shows in 12 steps the manner in which an openend of a metal cylinder 5 can be deformed by means of forming head 62 offorming machine 1 according to FIGS. 6 and 7. Step 1 shows the startingposition, wherein workpiece 5 is clamped down in a chuck 60. Said end,which has already undergone an operation and which has a smallerdiameter than the other part of cylinder 5, is then (step 2) deformed byrotating chuck 60 and placing the forming rollers 13, 19 into contactwith, respectively, the outer surface and the inner surface of cylinder5 and moving said rollers radially towards axis of rotation 61 and awayfrom axis of rotation 61, respectively (step 2), and subsequentlyadjusting assembly 12 a distance y in the Y-direction. Then the assembly12 is translated in the X-direction is continued (step 3), so that aneccentric, cylindrical portion 41 remains, which portion has a smallerdiameter than the original open end of cylinder 5 over a distance y.Then (step 4) the forming rollers 13, 19 are moved radially outwards andradially inwards, respectively, so that the contact between said rollers13, 19 and, respectively, the outer surface and the inner surface of thewall of cylinder 5 is broken. Assembly 12 is moved back into cylindricalportion 41 in the X-direction, to the X-position in the startingposition.

[0043] The above cycle is repeated by adjusting assembly 12 over adistance y (step 5, which is substantially identical to step 2) andtranslating assembly 12 in the X-direction (step 6, which issubstantially identical to step 3), wherein the diameter of thecylindrical portion 41 is further reduced.

[0044] Depending on the characteristics of the workpiece, steps 2-4 arerepeated until the desired reduction of the diameter and theeccentricity have been obtained, wherein the wall of the deformedportion may lie outside the circumference of the other part of thecylinder.

[0045] FIGS. 10-12 show a fourth embodiment of the forming machine 1according to the present invention, wherein workpiece 5 is not onlycapable of being rotated, but also of being pivoted about a pivot point65. To this end a chuck 66 is mounted in a slot 67 in a housing 68. Saidhousing 68 is rotatably mounted in a frame (not shown) and furthermorecomprises hydraulic cylinders 69, 70 for radial adjustment of chuck 66,a gauge (not shown) for measuring the radial movement of chuck 66, acounterweight 72 for balancing the whole and a gauge (not shown) formeasuring the pivoting of workpiece 5.

[0046]FIGS. 13 and 14 schematically show in 25 steps the manner in whichan open end of a metal cylinder 5 can be deformed by means of forminghead 3 of forming machine 1 according to FIG. 1. Step 1 shows thestarting position, wherein workpiece 5 is clamped down in a chuck 4.Said steps are similar to the steps of FIGS. 4 and 5, wherein themovement of pivot point 37 is effected by moving assembly 12 in theX-direction and the Y-direction.

[0047] As a matter of course the forming machines according to thepresent invention can be operated by a person as well as by a controlunit. Such a control unit is for example arranged for controlling themeans for moving the rollers in X-direction, Y-direction and radialdirection in accordance with a control programme that is stored in amemory, in such a manner that the forming rollers follow one or moredesired paths for deforming the workpiece into the desired product orintermediate product.

[0048] Although the invention has been explained on the basis of acylindrical metal workpiece in the foregoing, it is also possible toimplement the invention on workpieces of unround section, such as e.g.an oval, a substantially triangular or a multilobal section.

[0049] Consequently, the invention is not restricted to theabove-described embodiments, which can be varied in several ways withoutdeparting from the scope of the invention as defined in the claims.

1. A method for deforming a hollow workpiece (5) having at least oneopen end, wherein the workpiece (5) is clamped down in a clamping device(4; 60; 66), a first forming tool (13) is placed into contact with theouter surface of the workpiece (5), said workpiece (5) and said tool(13) are rotated about an axis of rotation (17) relative to each otherand the workpiece (5) is deformed by means of said first tool (13),characterized in that a second forming tool (19) is placed into thecavity defined by the workpiece (5), and into contact with the innersurface of the hollow workpiece (5), and the workpiece (5) is deformedby means of said second tool (19).
 2. A method according to claim 1,wherein said workpiece (5) on the one hand and said first and saidsecond tool (13, 19) on the other hand can be rotated relative to eachother about an axis of rotation (17) which extends eccentrically and/orat an angle with the central axis of the clamped-down workpiece (5). 3.A method according to claim 1 or 2, wherein said first and said secondtool (13, 19) rotate in at least substantially the same plane during atleast part of the operation.
 4. A method according to any one of thepreceding claims, wherein the clamping device (4; 60; 66) on the onehand and said tools (13, 19) on the other hand are pivoted about atleast one axis (37) relative to each other during said deformationand/or between deforming steps (on the same workpiece).
 5. A methodaccording to claim 4, wherein said clamping device (4; 60; 66) on theone hand and said tools (13, 19) on the other hand are pivoted about atleast two axes (37, 17) relative to each other during said deformationand/or between deforming steps wherein at least two of said axes (37,17), or the projections of each of said axes (37, 17) on a common plane,are at an angle with respect to each other.
 6. A method according toclaim 4 or 5, wherein at least one of said axes (37) is moved duringsaid deformation and/or between deforming steps.
 7. A method accordingto any one of the preceding claims, wherein the larger part of themachining is carried out in one flowing movement.
 8. A forming machine(1) at least comprising a clamping device (4; 60; 66) for clamping downa hollow workpiece (5) to be deformed, which has at least one open end,a first forming tool (13) which can be placed into contact with theouter surface of the workpiece (5) while the workpiece (5) is beingworked, and by means of which the workpiece (5) can be deformed ininward direction, driving means (25, 26, 28) for rotating said workpiece(5) and said tool relative to each other, in such a manner that saidtool can follow one or more desired paths with respect to the workpiece(5) so as to work said workpiece (5), characterized in that said formingmachine (1) comprises at least one second forming tool (19), which canbe introduced into the workpiece (5) and placed into contact with theinner wall of the workpiece (5), in such a manner that said wall can bedeformed outwards.
 9. A forming machine (1) according to claim 8,wherein said driving means (25, 26, 28) are capable of rotating saidworkpiece (5) on the one hand and said first and said second tool (13,19) on the other hand can be rotated relative to each other, about anaxis of rotation (17) which extends eccentrically and/or at an anglewith the central axis of the workpiece (5).
 10. A forming machine (1)according to claim 10, wherein said clamping device (4; 60; 66) on theone hand and said tools (13, 19) on the other hand are pivotablerelative to each other about at least one axis (37).
 11. A formingmachine (1) according to claim 10, wherein the clamping device (4; 60;66) on the one hand and the tools (13, 19) on the other hand arepivotable about at least two axes (37, 17), wherein at least two of saidaxes (37, 17), or a projection of said axes (37, 17) on a common plane,are at an angle with respect to each other.
 12. A forming machine (1)according to claim 10 or 11, wherein at least one of said axes (37) canbe moved.
 13. A forming machine (1) according to any one of the claims8-12, wherein the clamping device (4; 60; 66) for the work piece (5) canbe rotated.
 14. A forming machine (1) according to claim 13, wherein achuck (66) for clamping down the workpiece (5) is pivotally andtranslatably mounted in said clamping device.
 15. A hollow workpiece (5)having a continuous wall and at least one open end, which has beendeformed, preferably by means of the method according to any one of theclaims 1-7, wherein at least part of the edge of said end lies outsidethe circumference of the workpiece (5) after deformation.
 16. Aworkpiece according to claim 15, comprising a substantially cylindricalor oval metal body (5) having two substantially cylindrical or oval openends, which have been deformed in such a manner that at least part ofthe edge of at least one of the two ends lies outside the circumferenceof an undeformed portion of the workpiece, wherein the projections ofthe central axes of said ends on a plane straight through an undeformedpart of the metal body are at an angle of less than 180° with respect toeach other.
 17. A catalytic converter for a vehicle, such as e.g. a car,comprising a workpiece according to claim 15 or 16.